Architecture is used for certain in any enterprise. The question is if the right architecture is being used. Well in fact there isn’t such thing as “the right architecture”. The right information, system or infrastructure architecture depends on two aspects:
1) The business needs and the requirements of the enterprise.
2) Cross enterprise view of the current data, system and infrastructure.
By analyzing those two aspects one can determine if given architecture is really the right one for the enterprise. The process of analyzing the current an the target business, information, system and infrastructure architecture together with gap analysis and set of standard and rules to fulfill the target architecture is actually called Enterprise Architecture (EA).
Without EA you can’t tell for sure that your IT investments really address all the enterprise business requirements. Without performing EA process you don’t get real view of those two aspects though, you can’t tell for sure that given system architecture is the “right one”.